// MIT License

// Copyright (c) 2019 Erin Catto

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#include "test.h"
#include "imgui/imgui.h"

/// This test shows how a distance joint can be used to stabilize a chain of
/// bodies with a heavy payload. Notice that the distance joint just prevents
/// excessive stretching and has no other effect.
/// By disabling the distance joint you can see that the Box2D solver has trouble
/// supporting heavy bodies with light bodies. Try playing around with the
/// densities, time step, and iterations to see how they affect stability.
/// This test also shows how to use contact filtering. Filtering is configured
/// so that the payload does not collide with the chain.
class WreckingBall : public Test
{
public:
  WreckingBall()
  {
    b2Body* ground = NULL;
    {
      b2BodyDef bd;
      ground = m_world->CreateBody(&bd);

      b2EdgeShape shape;
      shape.SetTwoSided(b2Vec2(-40.0f, 0.0f), b2Vec2(40.0f, 0.0f));
      ground->CreateFixture(&shape, 0.0f);
    }

    {
      b2PolygonShape shape;
      shape.SetAsBox(0.5f, 0.125f);

      b2FixtureDef fd;
      fd.shape = &shape;
      fd.density = 20.0f;
      fd.friction = 0.2f;
      fd.filter.categoryBits = 0x0001;
      fd.filter.maskBits = 0xFFFF & ~0x0002;

      b2RevoluteJointDef jd;
      jd.collideConnected = false;

      const int32 N = 10;
      const float y = 15.0f;
      m_distanceJointDef.localAnchorA.Set(0.0f, y);

      b2Body* prevBody = ground;
      for (int32 i = 0; i < N; ++i)
      {
        b2BodyDef bd;
        bd.type = b2_dynamicBody;
        bd.position.Set(0.5f + 1.0f * i, y);
        if (i == N - 1)
        {
          bd.position.Set(1.0f * i, y);
          bd.angularDamping = 0.4f;
        }

        b2Body* body = m_world->CreateBody(&bd);

        if (i == N - 1)
        {
          b2CircleShape circleShape;
          circleShape.m_radius = 1.5f;
          b2FixtureDef sfd;
          sfd.shape = &circleShape;
          sfd.density = 100.0f;
          sfd.filter.categoryBits = 0x0002;
          body->CreateFixture(&sfd);
        }
        else
        {
          body->CreateFixture(&fd);
        }

        b2Vec2 anchor(float(i), y);
        jd.Initialize(prevBody, body, anchor);
        m_world->CreateJoint(&jd);

        prevBody = body;
      }

      m_distanceJointDef.localAnchorB.SetZero();

      float extraLength = 0.01f;
      m_distanceJointDef.minLength = 0.0f;
      m_distanceJointDef.maxLength = N - 1.0f + extraLength;
      m_distanceJointDef.bodyB = prevBody;
    }

    {
      m_distanceJointDef.bodyA = ground;
      m_distanceJoint = m_world->CreateJoint(&m_distanceJointDef);
      m_stabilize = true;
    }
  }

  void UpdateUI() override
  {
    ImGui::SetNextWindowPos(ImVec2(10.0f, 100.0f));
    ImGui::SetNextWindowSize(ImVec2(200.0f, 100.0f));
    ImGui::Begin("Wrecking Ball Controls", nullptr, ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize);

    if (ImGui::Checkbox("Stabilize", &m_stabilize))
    {
      if (m_stabilize == true && m_distanceJoint == nullptr)
      {
        m_distanceJoint = m_world->CreateJoint(&m_distanceJointDef);
      }
      else if (m_stabilize == false && m_distanceJoint != nullptr)
      {
        m_world->DestroyJoint(m_distanceJoint);
        m_distanceJoint = nullptr;
      }
    }

    ImGui::End();
  }

  void Step(Settings& settings) override
  {
    Test::Step(settings);

    if (m_distanceJoint)
    {
      g_debugDraw.DrawString(5, m_textLine, "Distance Joint ON");
    }
    else
    {
      g_debugDraw.DrawString(5, m_textLine, "Distance Joint OFF");
    }
    m_textLine += m_textIncrement;
  }

  static Test* Create()
  {
    return new WreckingBall;
  }

  b2DistanceJointDef m_distanceJointDef;
  b2Joint* m_distanceJoint;
  bool m_stabilize;
};

static int testIndex = RegisterTest("Examples", "Wrecking Ball", WreckingBall::Create);
